(6 and 10 percent, respectively), Cytophaga-Flexibacter-Bacteroides (19 percent), high-G+C-content gram-positive organisms (Actinobacteria; 25 percent), and low-G+C-content gram-positive organisms (Bacillus and Clostridium; 19 percent). Twelve percent were identified as chloroplasts. The remaining 9 percent represented beta- and delta-Proteobacteria, Verrucomicrobiales, and candidate divisions. In contrast to the alkaliphilic Mono Lake, the acidic Rio Tinto River is host to communities that are dominated by microeukaryotes.40 It is very important to study the behavior of chemical and isotopic biosignatures over the full range of possible environmental conditions identified on Mars in order to best apply biosignature methods to Mars samples, both in situ and returned samples.
With each new discovery from the exploration of Mars using orbiters and surface rovers comes the possiblility for newly defined Earth analogs. Most recently, findings from the MERs and Mars Express have expanded the suite of relevant Earth analogs to include sulfate-rich evaporite sediments, acidic aqueous systems hosting key indicator minerals found on Mars (e.g., jarosite, alunite), and Noachian-like systems.
An obvious development that would advance Mars astrobiology is precision landing of spacecraft. Landing uncertainties have decreased considerably with each landed mission (e.g., the 80- by 12-km landing ellipses of the MERs are expected to shrink to a 20-km circle for the Mars Science Laboratory (MSL)). However, astrobiology targets, such as sites of hydrothermal or fluvial activity, are likely to be small and dispersed, and better landing precision will be required to visit such locations. Similarly, implementing a robust strategy of caching samples for potential retrieval at a later date requires the development of a capability to land a spacecraft within a kilometer or less of a given point on Mars. Landing higher-mass payloads at high surface elevations requires additional development of entry, descent, and landing technology.41
The development of instruments for in situ measurements to address astrobiology goals is especially critical. Individual instruments are normally developed for specific missions, and there are few, if any, appropriate instruments at sufficient readiness levels currently “on the shelf.” Advances in appropriate technologies are proceeding rapidly, but there is a significant lag time in applying these new techniques to spaceflight missions. This stems in part from the special requirements that spaceflight imposes (miniaturization, modest power requirements, thermal and shock loading), but also from NASA’s lack of funding for instrument development, especially within the Astrobiology program.
As noted in an earlier chapter, the identification of poorly crystalline minerals or amorphous phases may require more advanced analytical techniques, building on the success of the MSL-designed ChemCam. Analysis of trace elements and stable isotope ratios in minerals and extracted organic matter, which is not possible with current flight instruments, also requires new technology. Improvements in imaging technology are needed for in situ examination of morphologies at submicroscopic scales. Especially important for implementation of the Astrobiology Field Laboratory may be further advances in sampling handling and processing dealing with the extraction and analysis of organic matter, with appropriate measures taken to ensure compliance with relevant planetary protection regulations. Analyses of gradients in chemistry and oxidation states in rocks are key measurements for astrobiology, and development of in situ methods having increased spatial resolution may be required. Other examples of instruments that could be developed for astrobiology are discussed in the section “In Situ Analyses Related to Life Detection” above.
Geochronology using radiogenic isotopes is an extremely challenging task, and remote sensing measurements are unlikely to provide precise or unambiguous age determinations. Absolute age data are necessary for assessment of a site’s geological history. Crater-density data provide only relative ages, and these may not be reliable in some cases because of cycles of burial and exhumation.42 If suitable remote-sensing or in situ techniques are not available, age determinations may require the return of samples.
Despite successes in locating global and regional subsurface hydrogen (presumably ice) using gamma-ray detection (Mars Odyssey) and potentially radar sounding (Mars Reconnaissance Orbiter), methods must be developed for local electromagnetic sounding for subsurface water at specific sites. Drilling technology or other means to access subsurface fluids and rocks may be necessary, although horizontal mobility is, perhaps, more important than vertical access.